ORIGINAL PAPER

Synthesis and characterization of thermostable polyamidesfrom unsymmetrical diamines containing flexibleether linkage and different diarylimidazole pendantsin ionic liquids

Mousa Ghaemy & Seyed Mojtaba Amini Nasab &

Mehdi Taghavi & Marjan Hassanzadeh

Received: 13 March 2012 /Accepted: 29 May 2012# Springer Science+Business Media B.V. 2012

Abstract A series of aromatic poly(amide-ether) (PAE)scontaining derivatives of imidazole heterocyclic ring andflexible ether linkages was synthesized from polymerizationreaction of three new diamines with commercially availablearomatic diacids by using two different methods of directpolycondensation: (1) By using triphenyl phosphite (TPP)as activating agent, NMP, pyridine (Py) and LiCl, and (2) byusing combination of an ionic liquid (IL) and TPP whichallowed to carry out PAEs synthesis without using Py, LiCland NMP. Room temperature ILs bearing anions such asBF4

-, Br-, Cl-, and PF6- with symmetrical 1,3-dialkylimida-

zolium cations have been prepared and used as polyconden-sation media. The polymers were obtained in good yieldswith moderate viscosity (0.47–0.68 dL/g) in a shorter timeof reaction (2.5 h) in comparison with the PAEs obtained inNMP (12 h). All of these polymers were amorphous innature, showed excellent solubility in amide-type polaraprotic solvents. These polymers showed good thermal sta-bility with glass transition temperatures (Tg) between 212–355 °C and 10 % weight loss temperatures were recordedaround 421 °C and 460 °C in air and N2, respectively. Thesepolymers showed blue flourescence emission in the range of460–505 nm and can be candidate for applications in photo-luminescent devices.

Keywords Polyamides . Ionic liquids . Thermal stability .

Solubility . High performance polymers

Introduction

In recent years much attention has been given to reusabilityof solvents and catalysts for the development of cost-effective protocols [1–4]. The ambient temperature ionicliquids especially those based on 1,3-dialkylimidazoliumcations have gained considerable interest as promising al-ternative green solvents in polymer synthesis [5]. Analyzingthe application of ILs in polymer synthesis proves theirefficiency, so various polycondensation processes were suc-cessfully accomplished in ionic medium as well. There havebeen many reports that the reaction of different diamineswith dicarboxylic acids in ILs resulted in the formation ofhigh molecular weight polyamides [6–10]. Imidazolium-based ILs has been significantly expanded so that todaymany different candidates are accessible and even commer-cially available. The miscibility of ILs with other solventscan also be controlled, through a careful choice of the ions,making them attractive as easily containable solvents. Insuch a system, the advantages of both homogeneous andheterogeneous catalysis, good catalyst efficiency under mildreaction conditions and facile catalyst recovery, respective-ly, can be combined [11–13]. Aromatic polyamides are usedin applications demanding service at enhanced temperaturewhile maintaining their structural integrity and an excellentcombination of chemical, physical and mechanical proper-ties. However, these polyamides encounter processing diffi-culty due to their infusibility and poor solubility in organicsolvents [14–19]. The reasons for processing difficulty areinherent macromolecular rigidity, strong interchange forces,or semicrystallinity. Many studies have attempted to en-hance their solubility and processability by introducingbulky side groups or flexible chains into the polyamidebackbone, or breaking its symmetry and regularity, or

M. Ghaemy (*) : S. M. A. Nasab :M. Taghavi :M. HassanzadehPolymer Chemistry Research Laboratory,Department of Chemistry, University of Mazandaran,Babolsar 47416-95447 IR, Irane-mail: ghaemy@umz.ac.ir

J Polym Res (2012) 19:9905DOI 10.1007/s10965-012-9905-6

destroying the hydrogen bonding by N-substitution withcertain groups such as methyl. These can increase the flex-ibility, lower the melt point, and improve the solubility ofpolymers [20–34]. The combination of these elements in thechemical structures of polymers can also provide improvedcharacteristics for special applications, for which polyamidecontaining these sequences have exhibited particularly goodproperties.

In this paper, we wish to report a convenient and envi-ronmentally benign green route for the synthesis of novelhigh-performance PAEs by using imidazolium-based ILsunder classical heating conditions. Therefore, three newasymmetric diamines containing derivatives of imidazoleheterocyclic ring and flexible ether linkages namely: 4-(3-(4-aminophenoxy)-4-(4,5-diphenyl-1 H-imidazol-2-yl)phe-noxy)benzenamine, 4-(3-(4-aminophenoxy)-4-(4,5-diphenyl-1 H-imidazol-2-yl)phenoxy)benzenamine, 4-(3-(4-aminophenoxy)-4-(4,5-diphenyl-1 H-imidaz -ol-2-yl)phenoxy)benzenamine, were synthesized. These diamineswere used for the synthesis of novel PAEs in view ofimproving their solubility with outstanding thermal stability.The collection of functional groups of flexible, unsymmet-rical, and bulky pendants in the backbone of these polymerswill be expected to decrease the regularity of polymerchains, weaken the intermolecular intractions and chainpacking efficiency, increase the barrier for free rotationand Tg and thermal stability, and afford useful photophysicalproperties.

Experimental

Materials

All chemicals were purchased from Fluka and Merck Chem-ical Co. (Germany) through a local agency. Ammonium ace-tate, hydrazine monohydrate and 10 % palladium on activatedcarbon were used as received. N-methyl-2-pyrrolidone(NMP), N,N-dimethylacetamide (DMAc), and pyridine (Py)were purified by distillation under reduced pressure overcalcium hydride and stored over 4 Å molecular sieves.

Ionic liquids synthesis

All room temperature ILs were prepared by using proce-dures reported in the literature [13]. The structure of theprepared ILs was given in Table 1, and they were all veryviscose liquids at room temperature.

Monomer synthesis

The synthetic pathway leading to the synthesis of targetdiamines is outlined in Scheme 1.

Synthesis of 2,4-bis(4-nitrophenoxy)benzaldehyde

A mixture of 1.38 g (10 mmol) 2,4-dihydroxy benzalde-hyde, 2.82 g (20 mmol) 1-fluoro-4-nitrobenzene, and2.76 g (20 mmol) anhydrous potassium carbonate in10 mL dry DMSO was refluxed at 120 °C for 12 h. Aftercompletion of the reaction (as witnessed by TLC test), themedium was cooled to room temperature. The reactionmixture was poured into 400 mL deionized water. Theresulting yellowish powder was then collected by filtration,washed with water several times and dried in vacuum ovenat 80 °C. This crude product was purified by recrystalliza-tion from ethanol. The yield of the reaction was 93 %(3.55 g), and the melting point was 152–156 °C. FT-IR(KBr disk, cm−1): 3105 (C-H aromatic, stretching), 2842(C-H aldehyde, stretching), 1684 (C0O aldehyde, stretch-ing), 1583 (C0C stretching), 1522, 1350 (NO2, symmetri-cal and unsymmetrical stretching) and 1229 (C-O-C,stretching). 1H NMR (400 MHz, DMSO-d6, δ in ppm):7.08 (d, 1 H, Ar-H, J02 Hz), 7.19 (dd, 1 H, Ar-H, J08 Hz), 7.29–7.38 (m, 4 H, Ar-H), 8.03 (d, 1 H, Ar-H, J08.5 Hz), 8.26–8.34 (m, 4 H, Ar-H), 10.16 (s, 1 H, C-Haldehyde). Elemental analysis calculated for C19H12N2O7:C, 60.00 %; H, 3.18 %; N, 7.37 % and found: C, 59.98 %;H, 3.55 %; N, 7.32 %.

Synthesis of dinitro compounds

In a 500 mL round-bottomed two-necked flask equippedwith a condenser, magnetic stirrer bar and a nitrogen gasinlet tube, a mixture of 0.01 mol, 2,4-bis(4-nitrophenoxy)benzaldehyde, 0.01 mol diketone, 0.07 mol ammoniumacetate and 50 mL glacial acetic acid was refluxed for24 h. Upon cooling, the precipitate was collected by filtra-tion and washed with ethanol and water.

2-(2,4-bis(4-nitrophenoxy)phenyl)-1H-phenanthro[9,10-d]imidazole (A)

Yield 91 % and mp0225–227 °C. FT-IR (KBr disk, cm−1):3450 (N-H, stretching), 3076 (C-H aromatic, stretching),1609 (C0N, stretching), 1584 (C0C, stretching), 1531,1352 (NO2, symmetrical and unsymmetrical stretching),and 1263 (C-O-C, stretching). 1H NMR (DMSO-d6, δ inppm): 6.58 (d, 1 H, Ar-H, J02.2 Hz), 7.17 (d, 1 H, Ar-H, J08.2 Hz), 7.27 (d, 2 H, Ar-H, J08.8 Hz), 7.34–7.40 (m, 4 H,Ar-H), 7.57–7.73 (m, 4 H, Ar-H), 8.19 (d, 2 H, Ar-H, J08.2 Hz), 8.31 (d, 2 H, Ar-H, J08.2 Hz), 8.37 (d, 2 H, Ar-H,J08.4 Hz), 8.81 (dd, 1 H, Ar-H, J08.0 Hz), 13.38 (s, 1 H,N-H imidazole ring). Elemental analysis calculated forC33H20N4O6: C, 69.72 %; H, 3.52 %; N, 9.86 % and found:C, 69.66 %; H, 3.62 %; N, 9.85 %.

Page 2 of 13 J Polym Res (2012) 19:9905

8-(2,4-bis(4-nitrophenoxy)phenyl)-7H-acenaphtho[1,2-d]imidazole (B)

Yield 85 % and mp0260–263 °C. FT-IR (KBr disk, cm−1):3460 (N-H, stretching), 3075 (C-H aromatic, stretching),1609 (C0N, stretching), 1589 (C0C, stretching), 1527,1351 (NO2, symmetrical and unsymmetrical stretching),and 1260 (C-O-C, stretching). 1H NMR (DMSO-d6, δ inppm): 6.54 (d, 1 H, Ar-H, J02.4 Hz), 6.69 (dd, 1 H, Ar-H,J08.4 Hz), 7.22 (d, 2 H, Ar-H, J08.2 Hz), 7.43 (d, 1 H, Ar-H, J08.4 Hz), 7.51 (d, 2 H, Ar-H, J08.2 Hz), 7.64 (d, 1 H,Ar-H, J07.6 Hz), 7.75 (d, 1 H, Ar-H, J07.6 Hz), 7.86 (dd,2 H, Ar-H, J08.0 Hz), 7.91 (d, 2 H, Ar-H, J08.0 Hz), 8.31(d, 2 H, Ar-H, J08.2 Hz), 8.45 (d, 2 H, Ar-H, J08.2 Hz),

13.64 (s, 1 H, N-H imidazole ring). Elemental analysiscalculated for C31H18N4O6: C, 68.63 %; H, 3.32 %; N,10.32 % and found: C, 68.51 %; H, 3.42 %; N, 10.27 %.

2- (2,4-bis(4-nitrophenoxy)phenyl)-4,5-diphenyl-1H-imidazole (C)

Yield 93 % and mp0193–195 °C. FT-IR (KBr disk, cm−1):3452 (N-H, stretching), 3067 (C-H aromatic, stretching),1611 (C0N, stretching), 1588 (C0C, stretching), 1532,1350 (NO2, symmetrical and unsymmetrical stretching),and 1267 (C-O-C, stretching). 1H NMR (DMSO-d6, δ inppm): 6.14 (d, 1 H, Ar-H, J08.2 Hz), 6.38 (s, 1 H, Ar-H),6.71 (d, 1 H, Ar-H, J08.2 Hz), 7.17–7.39 (m, 14 H, Ar-H),

Scheme 1 Synthesis of target diamines (D-F)

Table 1 The influence of IL cation and anion upon yield and molecular weight (ηinh) of PAE1a

Polymer IL Code Yield (%) ηinha

PAE1a 1,3-dipropyl imidazolium bromide [1,3-Pr2im]Br 95 0.62

PAE1a 1,3-diisopropyl imidazolium bromide [1,3-Isopr2im]Br 93 0.62

PAE1a 1,3-dibutyl imidazolium bromide [1,3-Bu2im]Br 86 0.55

PAE1a 1,3-dipentyl imidazolium bromide [1,3-Pent2im]Br 79 0.55

PAE1a 1,3-dihexyl imidazolium bromide [1,3-Hex2im]Br 76 0.49

PAE1a 1,3-diheptyl imidazolium bromide [1,3-Hep2im]Br 75 0.49

PAE1a 1,3-dibutyl imidazolium tetrafluoroborate [1,3-Butyl2im]BF4 70 0.44

PAE1a 1,3-dibutyl imidazolium hexafluorophosphate [1,3-Butyl2im]PF6 62 0.39

a Measured at a concentration of 0.5 g/dL in NMP at 25 °C

J Polym Res (2012) 19:9905 Page 3 of 13

8.17–8.37 (m, 4 H, Ar-H), 13.67 (s, 1 H, N-H imidazolering). Elemental analysis calculated for C33H22N4O6: C,69.47 %; H, 3.86 %; N, 9.82 % and found: C, 69.33 %; H,3.96 %; N, 9.79 %.

Synthesis of diamine compounds

In a 250 mL round-bottomed three-necked flask equippedwith a dropping funnel, a reflux condenser and a magneticstirrer bar, 0.01 mol dinitro (A–C) and 0.2 g palladium onactivated carbon (Pd/C, 10 %), were dispersed in 80 mLethanol. The suspension solution was heated to reflux, and8 mL of hydrazine monohydrate was added slowly to themixture. After a further 5 h of reflux, the solution wasfiltered hot to remove Pd/C, and the filtrate was cooled togive crystals. The product was collected by filtration anddried in vacuum at 80 °C.

4,4′-(4-(1 H-phenanthro[9,10-d]imidazol-2-yl)-1,3-phenylene)bis(oxy)dianiline (D)

Yield 82 % and mp0173–175 °C. FT-IR (KBr disk, cm−1):3478, 3372 (NH2, stretching), 3443 (N-H imidazole ring,stretching), 3046 (C-H aromatic, stretching), 1637 (C0N,stretching), 1596 (C0C, stretching), and 1206 (C-O-C,stretching). 1H NMR (DMSO-d6, δ in ppm): 5.06 (s, 4 H,N-H), 6.48 (d, 1 H, Ar-H, J02.0 Hz), 6.66 (d, 4 H, Ar-H, J08.0 Hz), 6.71 (dd, 1 H, Ar-H, J08.0 Hz), 6.87 (d, 2 H, Ar-H,J08.0 Hz) , 6.99 (d, 2 H, Ar-H, J08.0 Hz), 7.61 (distorted d,2 H, Ar-H), 7.71 (distorted dd, 2 H, Ar-H), 8.18 (d, 1 H, Ar-H, J08.5), 8.64 (d, 2 H, Ar-H, J08.5 Hz), 8.81 (distorteddd, 2 H, Ar-H), 12.88 (s, 1 H, N-H imidazole ring). 13CNMR (400 MHz, DMSO-d6, δ in ppm): 104.68, 110.14,114.78, 115.17, 115.28, 121.49, 121.76, 122.37, 122.75,122.85, 124.16, 124.43, 125.53, 127.28, 127.42, 127.53,127.88, 131.31, 132.41, 136.82, 145.09, 145.28, 146.21,146.34, 146.36, 147.13, 158.06, 161.25. Elemental analysiscalculated for C33H24N4O2: C, 77.95 %; H, 4.72 %; N,11.02 % and found: C, 77.82 %; H, 4.84 %; N, 11.00 %.

4,4′-(4-(7 H-acenaphtho[1,2-d]imidazol-8-yl)-1,3-phenylene)bis(oxy)dianiline (E)

Yield 75 % and mp0180–183 °C. FT-IR (KBr disk, cm−1):3483, 3371 (NH2, stretching), 3440 (N-H imidazole ring,stretching), 3046 (C-H aromatic, stretching), 1633 (C0N,stretching), 1597 (C0C, stretching), and 1208 (C-O-C,stretching). 1H NMR (DMSO-d6, δ in ppm): 5.05 (s, 2H,N-H), 5.63 (s, 2H, N-H), 6.22 (dd, 1H, Ar-H, J08.0 Hz),6.31 (d, 1 H, Ar-H, J02.4 Hz), 6.61 (d, 2 H, Ar-H, J08.6 Hz) , 6.77 (d, 2 H, Ar-H, J07.6 Hz), 6.79 (d, 2 H, Ar-H,J07.6 Hz), 7.00 (d, 1 H, Ar-H, J08.8 Hz), 7.06 (d, 1 H, Ar-H, J07.0), 7.27 (d, 2 H, Ar-H, J08.0 Hz), 7.46 (dd, 1 H, Ar-

H, J08.0 Hz), 7.61 (dd, 1 H, Ar-H, J08.0 Hz), 7.81 (dd,2 H, Ar-H, J08.0 Hz), 7.89 (d, 1 H, Ar-H, J07.0 Hz), 12.60(s, 1 H, N-H imidazole ring). 13C NMR (400 MHz, DMSO-d6, δ in ppm): 104.59, 109.24, 114.86, 115.07, 115.12,121.51, 121.81, 122.42, 122.60, 122.91, 124.13, 124.55,125.61, 127.29, 127.37, 127.49, 127.89, 131.40, 132.53,136.71, 145.22, 146.04, 146.18, 148.23, 158.11, 161.15Elemental analysis calculated for C31H22N4O2: C,77.18 %; H, 4.56 %; N, 11.62 % and found: C, 77.11 %;H, 5.08 %; N, 11.58 %.

4-(3-(4-aminophenoxy)-4-(4,5-diphenyl-1H-imidazol-2-yl)phenoxy)benzenamine (F)

Yield of this product was 95 % and it turned dark at 168 °Cdue to oxidation of amine groups. FT-IR (KBr disk, cm−1):3472, 3368 (NH2, stretching), 3439 (N-H imidazole ring,stretching), 3047 (C-H aromatic, stretching), 1630 (C0N,stretching), 1597 (C0C, stretching), and 1212 (C-O-C, stretch-ing). 1H NMR (DMSO-d6, δ in ppm): 5.03 (s, 2 H, N-H), 5.41(s, 2 H, N-H), 6.12 (d, 1 H, Ar-H, J08 Hz), 6.34 (s, 1 H), 6.51(d, 2 H, Ar-H, J08.35 Hz) , 6.61 (d, 2 H, Ar-H, J08.35 Hz),6.7 (s, 1 H, Ar-H), 6.78 (d, 2 H, Ar-H, J08.35 Hz), 6.98 (d,2 H, Ar-H, J08.75), 7.18–7.32 (m, 10 H, Ar-H), 13.61 (s, 1 H,N-H imidazole ring). 13C NMR (400 MHz, DMSO-d6, δ inppm): 104.62, 107.35, 108.33, 114.81, 115.69, 122.34,124.96, 126.87, 127.67, 127.84, 129.29, 129.40, 129.94,130.77, 131.78, 132.21, 134.03, 134.05, 145.31, 145.53,145.61, 146.81, 150.21, 160.35, 161.39. Elemental analysiscalculated for C33H26N4O2: C, 77.65 %; H, 5.10 %; N,10.98 % and found: C, 77.61 %; H, 5.18 %; N, 10.35 %.

Polymer synthesis

Method I: direct polycondensationusing TPP/ NMP/Py/LiCl

The following general procedure was used for the prepara-tion of PAEs from the diamines D-F and various aliphaticand aromatic dicarboxylic acids. Into a 50 mL three-neckedround-bottomed flask equipped with a condenser, a mechan-ical stirrer and a nitrogen gas inlet tube, diamine (D-F)(1 mmol), a dicarboxylic acid (1 mmol), and LiCl (0.30 g)were dissolved in a mixture of Py (1 mL), TPP (1.20 mmol),and NMP (5 mL). The mixture was heated at 120 °C for12 h with stirring under dry N2 atmosphere. The reactionmixture was then cooled to room temperature and the result-ing polymer was precipitated in 200 mL methanol. The pre-cipitate was filtered and washed with hot water, and then wasfurther purified by washing with refluxing methanol for 24 hin a Soxhlet apparatus to remove the low molecular weightolygomers. The inherent viscosity of the resulting PAE3a′-

Page 4 of 13 J Polym Res (2012) 19:9905

PAE1c′ was measured at a concentration of 0.5 g/dL in NMPat 25 °C and were in the range of 0.41–0.65 dL/g.

Method II: direct polycondensation using TPP/ILs

The following general procedure, as illustrated in Scheme 2,was used for the preparation of PAEs from the diamine andvarious aliphatic and aromatic dicarboxylic acids.

Into a 50 mL three-necked round-bottomed flask fittedwith a water cooled condenser, a mechanical stirrer and anitrogen gas inlet tube, a mixture of diamine (D-F) (1 mmol),terphthalic acid (1 mmol, 0.166 g), 1,3-dipropyl imidazo-lium bromide {[1,3-(pr)2im]Br} (0.70 g), and TPP(1.29 mmol)) was placed. The mixture was heated at 110 °Cfor 2.5 h. As the reaction proceeded, the solution becameviscous. The reaction mixture was then cooled to room tem-perature and the resulting polymers were precipitated in100 mL methanol. The precipitate was filtered and washedwith hot water, and then was further purified by washing withrefluxing methanol for 24 h in a Soxhlet apparatus to removethe low molecular weight oligomers. The inherent viscosity ofthe resulting PAEs was between 0.47–0.68 dL g−1, measuredat a concentration of 0.5 g/dL in NMP at 25 °C. The aboveprocedure was used for the preparation of all other PAEs.

PAE1a Yield 95 % and ηinh (dL/g)00.62. FT-IR (KBrdisk, cm−1): 3361 (N-H amide, stretching), 3047 (C-Haromatic, stretching), 1662 (C0O amide, stretching), 1604(C0N, stretching), 1513 (C0C, stretching) and 1266 (C-O-C,stretching). 1H NMR (400 MHz, DMSO-d6, δ in ppm): 6.70(distorted s, 1 H, Ar-H), 6.94 (distorted s, 1 H, Ar-H), 7.21 (d,4 H, Ar-H, J08.20 Hz), 7.65–7.90 (m, 8 H, Ar-H), 8.13 (dd,2 H, Ar-H, J08.40 Hz), 8.20 (d, 1 H, Ar-H, J08.00Hz), 8.44–8.57 (m, 4 H, Ar-H), 8.87 (s, 2 H, Ar-H), 10.44 (s, 1 H, N-Hamide), 10.54 (s, 1 H, N-H amide), 13.28 (s, 1 H, N-Himidazole ring). Elemental analysis calculated for(C41H26N4O4)n: C, 77.12 %; H, 4.07 %; N, 8.78 %. Found:C, 76.63 %; H, 4.51 %; N, 8.64 %.

PAE1b Yield 88 % and ηinh (dL/g)00.54. FT-IR (KBrdisk, cm−1): 3359 (N-H amide), 3064 (C-H aromatic),1685 (C0O amide), 1608 (C0N), 1522 (C0C) and 1266(C-O-C). 1H NMR (400 MHz, DMSO-d6, δ in ppm): 6.17(d, 1 H, Ar-H), 6.47 (s, 1 H, Ar-H), 6.72 (d, 1 H, Ar-H),7.13–7.40 (m, 14 H, Ar-H), 7.82–8.34 (m, 5 H, Ar-H),10.94 (s, 1 H, N-H amide), 11.11 (s, 1 H, N-H amide),13.04 (s, 1 H, N-H imidazole ring). Elemental analysiscalculated for (C40H25N5O4)n: C, 75.12 %; H, 3.91 %; N,10.95 %. Found: C, 75.96 %; H, 4.72 %; N, 8.84 %.

PAE1c Yield 90 % and ηinh (dL/g)00.52. FT-IR (KBrdisk, cm−1): 3368 (N-H amide), 3054 (C-H aromatic),2929 (C-H aliphatic), 1661 (C0O amide), 1607 (C0N),1505 (C0C) and 1259 (C-O-C). 1H NMR (400 MHz,DMSO-d6, δ in ppm): 1.25 (m, 8 H, C-H), 1.55 (m, 4 H,C-H), 2.25 (t, 4 H, C-H), 6.58 (s, 1 H, Ar-H), 6.84 (distorteds, 1 H, Ar-H), 7.08 (d, 2 H, Ar-H, J07.2 Hz), 7.18 (d, 2 H,Ar-H, J08.2 Hz), 7.63 (m, 8 H, Ar-H), 8.14 (d, 1 H, Ar-H,J08.4 Hz), 8.63 (d, 2 H, Ar-H, J07.6 Hz), 8.88 (distorted s,2 H, Ar-H), 9.92 (s, 1 H, N-H amide), 9.99 (s, 1 H, N-Hamide), 13.16 (s, 1 H, N-H imidazole ring). Elementalanalysis calculated for (C43H38N4O4)n: C, 76.56 %; H,5.64 %; N, 8.31 %. Found: C, 75.00 %; H, 6.59 %; N,8.09 %.

PAE2a Yield 86 % and ηinh (dL/g)00.49. FT-IR (KBrdisk, cm−1): 3362 (N-H amide), 3047 (C-H aromatic),1663 (C0O amide), 1604 (C0N), 1516 (C0C) and1260 (C-O-C). 1H NMR (400 MHz, DMSO-d6, δ inppm): 6.72 (distorted s, 1 H, Ar-H), 6.91 (distorted s,1 H, Ar-H), 7.25 (d, 4 H, Ar-H, J08.20 Hz), 7.68–7.99(m, 6 H, Ar-H), 8.13 (dd, 2 H, Ar-H, J08.40 Hz), 8.22 (d,1 H, Ar-H, J08.00 Hz), 8.43–8.57 (m, 4 H, Ar-H), 8.88 (s,2 H, Ar-H), 10.43 (s, 1 H, N-H amide), 10.56 (s, 1 H, N-Hamide), 13.24 (s, 1 H, N-H imidazole ring). Elementalanalysis calculated for (C39H24N4O4)n: C, 76.47 %; H,3.92 %; N, 9.15 %. Found: C, 76.63 %; H, 4.51 %; N,8.64 %.

Scheme 2 Polycondensation reaction of diamines (D-F) with different dicarboxylic acids

J Polym Res (2012) 19:9905 Page 5 of 13

PAE2b Yield 78 % and ηinh (dL/g)00.50. FT-IR (KBrdisk, cm−1): 3358 (N-H amide), 3072 (C-H aromatic), 1689(C0O amide), 1603 (C0N), 1528 (C0C) and 1262 (C-O-C).1H NMR (400 MHz, DMSO-d6, δ in ppm): 6.24 (d, 1 H,Ar-H), 6.49 (s, 1 H, Ar-H), 6.78 (d, 1 H, Ar-H), 7.14–7.44(m, 12 H, Ar-H), 7.86–8.33 (m, 5 H, Ar-H), 10.96 (s, 1 H,N-H amide), 11.17 (s, 1 H, N-H amide), 13.14 (s, 1 H, N-Himidazole ring). Elemental analysis calculated for(C38H23N5O4)n: C, 74.39 %; H, 3.75 %; N, 11.42 %.Found: C, 75.96 %; H, 4.72 %; N, 8.84 %.

PAE2c Yield 78 % and ηinh (dL/g)00.47. FT-IR (KBrdisk, cm−1): 3361 (N-H amide), 3059 (C-H aromatic), 2932(C-H aliphatic), 1665 (C0O amide), 1608 (C0N), 1501(C0C) and 1253 (C-O-C). 1H NMR (400 MHz, DMSO-d6,δ in ppm): 1.22 (m, 8 H, C-H), 1.54 (m, 4 H, C-H), 2.26 (t,4 H, C-H), 6.53 (s, 1 H, Ar-H), 6.84 (distorted s, 1 H, Ar-H),7.14 (d, 2 H, Ar-H, J07.2 Hz), 7.25 (d, 2 H, Ar-H, J08.2 Hz),7.66 (m, 6 H, Ar-H), 8.11 (d, 1 H, Ar-H, J08.4 Hz), 8.68 (d,2 H, Ar-H, J07.6 Hz), 8.82 (distorted s, 2 H, Ar-H), 9.91 (s,1 H, N-H amide), 10.07 (s, 1 H, N-H amide), 13.11 (s, 1 H, N-H imidazole ring). Elemental analysis calculated for(C41H36N4O4)n: C, 75.93 %; H, 5.55 %; N, 8.64 %. Found:C, 75.00 %; H, 6.59 %; N, 8.09 %.

PAE3a Yield 94 % and ηinh (dL/g)00.68. FT-IR (KBrdisk, cm−1): 3369 (N-H amide), 3043 (C-H aromatic),1665 (C0O amide), 1606 (C0N), 1514 (C0C) and 1268(C-O-C). 1H NMR (400 MHz, DMSO-d6, δ in ppm): 6.23 (d,1 H, Ar-H), 6.46 (s, 1 H, Ar-H), 6.74 (d, 1 H, Ar-H), 7.10–7.43(m, 14 H, Ar-H), 7.82 (m, 4 H, Ar-H), 8.07 (m, 4 H, Ar-H),10.47 (s, 1 H, N-H amide), 10.56 (s, 1 H, N-H amide), 12.99(s, 1 H, N-H imidazole ring). Elemental analysis calculated for(C41H28N4O4)n: C, 76.87 %; H, 4.37 %; N, 8.75 %. Found: C,76.63 %; H, 4.51 %; N, 8.64 %.

PAE3b Yield 90 % and ηinh (dL/g)00.54. FT-IR (KBrdisk, cm−1): 3360 (N-H amide), 3066 (C-H aromatic),1690 (C0O amide), 1603 (C0N), 1527 (C0C) and 1268(C-O-C). 1H NMR (400 MHz, DMSO-d6, δ in ppm): 6.20(d, 1 H, Ar-H), 6.46 (s, 1 H, Ar-H), 6.74 (d, 1 H, Ar-H),7.11–7.41 (m, 16 H, Ar-H), 7.89–8.32 (m, 5 H, Ar-H),10.99 (s, 1 H, N-H amide), 11.06 (s, 1 H, N-H amide),12.99 (s, 1 H, N-H imidazole ring). Elemental analysiscalculated for (C40H27N5O4)n: C, 76.55 %; H, 4.31 %; N,8.93 %. Found: C, 75.96 %; H, 4.72 %; N, 8.84 %.

PAE3c Yield 92 % and ηinh (dL/g)00.49. FT-IR (KBrdisk, cm−1): 3364 (N-H amide), 3050 (C-H aromatic), 2937(C-H aliphatic), 1666 (C0O amide), 1600 (C0N), 1508 (C0C)and 1255 (C-O-C). 1H NMR (400 MHz, DMSO-d6, δ inppm): 1.26 (m, 8 H, C-H), 1.55 (m, 4 H, C-H), 2.28 (t, 4 H,C-H), 6.14 (d, 1 H, Ar-H), 6.39 (s, 1 H, Ar-H), 6.64 (d, 1 H,

Ar-H), 6.98–7.40 (m, 14 H, Ar-H), 7.57–7.63 (dd, 4 H, Ar-H),9.94 (s, 1 H, N-H amide), 10.06 (s, 1 H, N-H amide), 13.06 (s,1 H, N-H imidazole ring). Elemental analysis calculated for(C43H40N4O4)n: C, 76.33 %; H, 5.92 %; N, 8.28 %. Found: C,75.00 %; H, 6.59 %; N, 8.09 %.

Measurements

Proton and carbon nuclear magnetic resonance (1H NMRand 13C NMR) spectra were recorded on a 400 MHz Bruker(Ettlingen, Germany) instrument using DMSO-d6 as solventand tetramethyl silane as an internal standard. Elementalanalyses performed by a CHN-600 Leco elemental analyzer.Melting point (uncorrected) was measured with a BarnsteadElectrothermal engineering LTD 9200 apparatus. Inherentviscosities (at a concentration of 0.5 g/dL) were measuredwith an Ubbelohde suspended-level viscometer at 25 °Cusing NMP as solvent. Qualitative solubility was deter-mined by using 0.05 g of the polymer in 0.5 mL of solvent.Thermogravimetric analysis (TGA) was performed with theDuPont Instruments (TGA 951) analyzer well equippedwith a PC at a heating rate of 10 °C/min under nitrogenand air. Differential scanning calorimeter (DSC) wasrecorded on a Perkin Elmer pyris 6 DSC under nitrogen(10 cm3/min) at a heating rate of 10 °C/min. Tg values wereread at the middle of the transition in heat capacity.Ultraviolet-visible and fluorescence emission spectra wererecorded on a Cecil 5503 (Cecil Instruments, Cambridge,UK) and Perkin-Elmer LS-3B spectrophotometers(Norwalk, CT, USA) (slit width 02 nm), respectively, usinga dilute polymer solution (0.10 g/dL) in NMP. X-ray powderdiffraction patterns were recorded by an X-ray diffractome-ter (GBC MMA instrument) with Be-filtered CuKα radia-tion (1.5418 A°) operating at 35.4 kV and 28 mA. The 2θscanning range was set between 4° and 50° at a scan rate of0.05° per second.

Results and discussion

Synthesis and characterization of diamine compounds

The aim of this study was the preparation of new thermallystable and organosoluble PAEs based on substituted imid-azole ring and ether linkage in the backbone of polymer.Therefore, these unsymmetrical diamines containing flexi-ble ether linkage and different bulky substituted imidazolering were synthesized, fully characterized, and used in poly-amides preparation. The compound 1, was successfullysynthesized from 1-fluoro-4-nitrobenzene and 2,4-dihy-droxy benzaldehyde as starting materials by the nucleophilicfluorodisplacement reaction according to the synthetic routeshown in Scheme 1. The structure of compound 1 was

Page 6 of 13 J Polym Res (2012) 19:9905

identified by elemental analysis, FT-IR and 1H NMR spec-troscopy. FT-IR spectrum of compound 1 showed peaks at1522 and 1350 cm−1 related to nitro groups, and 1H NMRspectrum of this compound showed signal at 10.16 ppm re-lated to C-H of aldehyde group. The reaction between com-pound 1 and phenanthrene-9,10-dione, acenaphthylene-1,2-dionephenantroquinone and benzil in the presence of ammo-nium acetate, which is well known as a classic but convenientsynthetic method for the preparation of imidazole ring, wasused to synthesize dinitro compounds (A-C). 1H NMRspectrum of dinitro compounds (A-C) showed the disappear-ance of signal at about 10 ppm which confirms the con-sumption of aldehyde group and a new peak in the region of13–14 ppm which is related to N-H of imidazole ring. Thediamine compounds (D-F) was obtained by catalytic reduc-tion of the intermediate dinitro compounds (A-C) by usinghydrazine hydrate and Pd/C in refluxing ethanol. The chem-ical structure and purity of compounds (D-F) was confirmedwith FT-IR, 1H and 13C NMR spectroscopic techniques andelemental analysis. The nitro groups of these compoundsyielded two characteristic absorption bands at about 1522and 1350 cm−1 (-NO2 asymmetric and symmetric stretch-ing). After reduction, these absorption peaks disappeared

and the primary amino group in compounds (D-F) showedthe typical absorption pair at 3350–3400 cm−1. As an ex-ample, the 1H NMR spectrum of diamine D, Fig. 1, con-firms that the nitro groups were completely transformed intothe amine groups by the high field shift of the aromaticprotons. The 1H NMR spectrum of this compound alsoshowed the characteristic resonance of amine groups at5.06 ppm. The DEPT and 13C NMR spectra of diamine D(Fig. 2a and b, respectively) showed 28 different carbons forthe aromatic segment and heterocyclic ring. It is interestingto mention that 13C NMR spectrum of compound 5 showsunsymmetric amine groups in respect to 4, 5-diphenyl imid-azole linkage.

Polymers synthesis and characterization

As part of our continuing attempts in developing high-performance and organosoluble polymers under green con-ditions, herein we wish to demonstrate a simple and efficientmethod for the polymerization of novel diamines with read-ily accessible dicarboxylic acids in imidazolium-based ILsas activator and solvent. The reaction proceeded efficientlywith IL/TPP as condensing agent without the need of any

Fig. 1 1H NMR spectrum of diamine (D) in DMSO-d6

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additional promoters, which are necessary upon utilizing oftraditional organic solvents like NMP. ILs, predominantlythose based on substituted imidazolium cations, which canbe prepared simply from the commercially available startingmaterial, N-trimethylsilylimidazole and alkyl halides wereused in this investigation. Thus, symmetrical 1,3-dialkyli-midazolium bromide with different alkyls and anions, aslisted in Table 1, were synthesized and used as polymeriza-tion reaction media. In order to optimize the reaction con-ditions, initially, the effect of ILs nature was studied. Theresults indicated that [1,3-Pr2im]Br is a better choice interms of yields and inherent viscosities (Table 1), thereforeit was selected for the synthesis of other PAEs. Although theresulting polymers are soluble in all of the mentioned ILs atthe reaction temperature, but, as alkyl chain in ILs increased,yields and inherent viscosities decreased. This may beexplained by the decrease of polarity and as a result, thelower mobility of polymers chain in longer alkyl chain ofILs. The synthetic procedure and polymers designation frompolymerization reaction of the diamines and various aliphat-ic and aromatic dicarboxylic acids are shown in Scheme 2.

When the same experiment was conducted in the presenceof NMP as a solvent, it took very long time (12 h) forcompletion of the reaction. Thus, notable rate of accelera-tion was observed in the presence of IL as a solvent. Thisdemonstrated the beneficial effect of IL as the solvent andactivator. It is shown that direct polycondensation is

Fig. 2 13C NMR spectra of diamine (D) in DMSO-d6: (I) DEPT and (II) normal

Fig. 3 Optimum conditions for the synthesis of PAE1a in IL

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successfully preceded in the mixture of ILs and TPP withoutusing any additional components such as CaCl2, LiCl, NMP,and pyridine. The optimum time of polycondensation wasdetermined for the preparation of PAE1a in the selected ILand temperature by measuring the yield and viscosity of thepolymer at different period of times. The results wereshown in Fig. 3. The structure of polymers was character-ized by means of elemental analysis, FT-IR and 1H NMR(400 MHz) spectroscopic techniques. The elemental analy-sis results were in good agreement with calculated percen-tages for carbon, hydrogen and nitrogen contents in PAEsrepeating units. The polymers were obtained as brownpowders with good yields (78–95 %) after extraction with

hot methanol, and their inherent viscosities were in therange of 0.37–0.68 dL/g indicating medium molecularweight. FT-IR spectra of these PAEs showed absorption ofamide N-H bond around 3200–3400 cm−1 (hydrogen band)and the peaks at 1670 cm−1 (C0O, amide) confirm the pres-ence of different carbonyl groups in the polymer. Figure 4shows a typical 1HNMR spectrum of PAE1c. The N-H protonof amide groups appeared in the region of 13.16 ppm whilethe N-H proton of imidazole ring appeared at 9.92 and9.99 ppm indicate that there are two different N-H groups inthe polymer backbone. The absorption of aromatic and ali-phatic protons appeared in the range of 6.58–8.88 ppm and1.25–2.25 ppm, respectively.

Fig 4 1H NMR spectrum of PAE1c in DMSO-d6

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Wide angle X-ray diffraction and solubility of PAEs

The representative x-ray diffractograms in Fig. 5 indicatethat all the PAEs are amorphous in nature and this can bemainly explained by the presence of bulky diarylimidazolependant. The amorphous nature of the PAEs was alsoreflecting their good solubility in common aprotic organicsolvents. However, the presence of imidazole and ethergroups in the pendent and in the main chain, respectively,can also contribute effectively in the solubility of thesepolymers by interacting with the polar molecules of sol-vents. The solubility behavior of the PAEs in several organicsolvents is summarized in Table 2. These polymersexhibited good solubility in a variety of solvents such as

NMP, DMAc, N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), pyridine, and m-cresol at room temper-ature or upon heating at 60 °C. This result demonstrated thatthe polymers containing benzil unit in the pendant, PAE3,displayed better solubility in the organic solvents in com-parison with other PAEs such as PAE1 and PAE2. Packingof the polymer chains is probably disturbed by the bulkypendent groups and consequently, the solvent molecules caneasily penetrate into the polymer chains. Among thesePAEs, PAE1 and PAE2 showed relatively lower solubilitydue to the presence of rigid biphenyl and naphthalene pen-dent groups in their backbone. PAE1 containing kink unitsshowed better solubility than PAE2. In addition, the solu-bility varies depending upon the dicarboxylic acid used. ThePAE was synthesized from aliphatic dicarboxylic acid(PAEc) exhibited better solubility behavior in less polarsolvents such as THF and m-cresol in comparsion withthose obtained from aromatic dicarboxylic acids. The meth-ylene units instead of rigid phenyl rings improved the solu-bility of this polymer.

UV-vis absorption and fluorescence characteristics

The photophysical properties of the PAEs were investigatedby UV-visible and fluorescence spectroscopy in NMP solu-tion. The absorption and fluorescence spectra of solution ofthe PAEs (0.1 g/dL) are shown in Fig. 6a and b, respectively,and the spectral data were listed in Table 3. These PAEsshowed strong UV absorption with the maximum wave-length at (λmax(ab)) 302–319 nm, which was assigned to π-π* transition resulting from the conjugation between the

Fig. 5 X-ray diffraction patterns of PAE(1–3)a

Table 2 Solubility of synthesized PAE1a- PAE3c

Code Solvent

Yield (%) ηinh (dL/g)b DMAc DMF NMP DMSO Py THF CHCl3 CH3CN m-cresol

PAE1a 95 0.62 ++ ++ ++ ++ + ± − − ±

PAE1b 88 0.54 ++ ++ ++ ++ + ± − − ±

PAE1c 90 0.52 ++ ++ ++ ++ ++ + − − +

PAE2a 86 0.49 ++ ++ ++ ++ ± − − − ±

PAE2b 78 0.50 ++ ++ ++ ++ ± − − − ±

PAE2c 78 0.47 ++ ++ ++ ++ + ± − − +

PAE3a 94 0.68 ++ ++ ++ ++ ++ ± − − +

PAE3b 90 0.54 ++ ++ ++ ++ ++ ± − − +

PAE3c 92 0.49 ++ ++ ++ ++ ++ + − − +

PAE3a′ 93 0.65 ++ ++ ++ ++ ++ ± − − +

PAE2b′ 72 0.41 ++ ++ ++ ++ + − − − −

PAE1c′ 83 0.49 ++ ++ ++ ++ + ± − − ±

++, soluble at room temperature; +, soluble on heating at 60 °C; ±, partially soluble on heating at 60 °C; −, insoluble on heating at 60 °Ca Measured at a polymer concentration of 0.5 g/dL in NMP at 25 °C

PAE1a-PAE3c and PAE3a′- PAE1c′ were synthesized in IL/TPP and NMP/TPP/Py/LiCl media, respectively

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aromatic rings and nitrogen atom in the pendent group. Aslightly red shift is observed in the spectra of PAEs insolution in comparison with the absorption spectra of thePAEs film (50 μm thick). The comparison of the absorptionspectra of PAE1, PAE2 and PAE3 show a discernible sim-ilarity demonstrating that the conjugated core is the absorb-ing unity. Figure 6b shows the emission spectra of the PAEsin dilute NMP solution. The excitation wavelength was310 nm in all cases. The fluorescence emission spectra ofthe PAEs exhibited peaks with maxima at 458–511 nm. Influorescence emission spectra PAE1 has higher intensity incomparison with other PAEs and the order is PAE1 > PAE3> PAE2. This can be due to restricted bond rotation inbiphenyl pendent group in PAE1 which without losing theexcited energy as heat much of this energy is available toemit as light. Low fluorescence intensity in PAE2 can alsobe due to the naphthalene pendant which is not conjugatedwith the imidazole chromophore. Moreover, the emissionintensity of aliphatic and aromatic PAEs was not exactly the

same which confirms that the fluorescence intensity is af-fected by incorporation of alkyl and phenyl groups into thepolymer main chain. To measure the photoluminescence (PL)quantum yields (Φf), dilute polymer solutions (0.2 g/dL) inNMP were prepared. A 0.10 N solution of quinine in H2SO4

(Φf00.53) was used as a reference [35]. The Φf values forPAEs were in the range of 7–35 %. The aliphatic polymersexhibited blue shift with higher quantum yield. The higher Φf

of aliphatic PAEs, PAEc, compared with the aromatic counter-parts, PAEa and PAEb, can be attributed to the effectivelyreduced conjugation and capability of charge-transfer com-plex formation by aliphatic diacids with the electron-donatingdiamine moiety in comparison with that of the strongerelectron-accepting aromatic diacids [36].

Thermal properties

DSC and TGA methods were applied to evaluate the ther-mal properties of the polymers. The DSC curves of thePAEs were recorded at heating rate of 10 °C/min in N2 areshown in Fig. 7. Melting endothermic peak was not ob-served in the DSC curves of PAEs which emphasize theamorphous nature of these polymers. The Tg values weretaken as the midpoint of the change in slope of the base lineof DSC curves, as shown in Table 4, were in the range 212–355 °C. As a general rule, the incorporation of bulky andrigid groups such as naphthalene pendant along a polymerbackbone restricts the free rotation of the macromolecularchains and leads to enhanced Tg values. Bond restriction inbiphenyl has also enhanced Tg values in PAE1 in compar-ison with PAE3. Conversely, the presence of flexible bondsuch as ether linkage in the main chain of these polymersreduced the rigidity of their backbones and consequently Tg

of these polymers to a reasonable and obtainable values inthe range of 212–355 °C. Therefore, Tg values of thesepolymers are affected by these two opposite key factors;restricted bond rotation by bulky pendants and flexibility of

Fig. 6 UV-vis and Fluorescence emission spectra of PAE(1–3)a and PAE(1–-3)c

Table 3 Optical properties data of PAE1a-PAE3c

Polymer λabs(nm)a λem(nm)a λabs(nm)b λem(nm)b Φf (%)c

PAE1a 315 500 317 505 13

PAE1b 318 496 319 499 15

PAE1c 304 461 305 466 35

PAE2a 316 504 318 511 7

PAE2b 319 498 319 501 8

PAE2c 307 467 308 471 20

PAE3a 314 495 315 498 9

PAE3b 317 495 318 497 12

PAE3c 302 458 303 460 28

Polymer concentration of 0.20 g/dL in NMPa,b UV-visible absorption and fluorescence emission spectra of thePAEs in solution (a) and in films (b), respectivelyc Fluorescence quantum yield relative to 10−5 M quinine sulfate in 1 NH2SO4 (aq) (Φf00.55) as a standard

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the main chain by ether linkages. The Tg values also dependon the flexibility of the diacid residue in the polymer mainchain. Among these polymers, PAEa based on terephthalicacid showed the highest Tg value and PAEc based on seba-cic acid showed the lowest Tg. Thermal stability of thesepolymers was evaluated by TGA in N2 and air atmosphereand the curves are shown in Fig. 8. The data, extracted fromthe original TGA curves, in Table 4 show the temperature of

10 % weight loss in the range of 460–493 °C and 421–480 °Cin N2 and air atmosphere, respectively. All of these polymersexhibited good thermal stability with insignificant weight lossup to 421 °C in air. The residual weights for the resulting PAEswere in the range of 25–78 % at 700 °C in N2. Char yield canbe used as criteria for evaluating limiting oxygen index (LOI)of the polymers in accordance with Van Krevelen andHoftyzer equation [37]. LOI 017.5+0.4 CR where CR0 charyield. For all the PAEs LOI values were calculated based ontheir char yields at 700 °C. Due to the reasons which havebeen explained above, the thermal stability of these PAEs areobserved in order of PAE2 > PAE1 > PAE3. According toTable 4, it is clear that aromatic PAEs have better thermalstability and higher LOI as compared to the aliphatic PAEs.This can be pertained to the rigid structure of aromaticdiacids compared to the flexible structure of aliphatic diac-ids. Therefore, the PAE1 and PAE3 have the highest andthe lowest thermal stability, respectively, which is due topresence of rigid phenyl and flexible aliphatic units in thetheir backbones.

Conclusions

In this study, imidazolium-based ILs have been used in asimple and efficient approach for the synthesis of photo-active and organosoluble high performance PAEs. A seriesof PAEs was prepared from three synthesized new diaminesand various commercially available dicarboxylic acids viadirect polycondensation by using combination of IL andTPP without using NMP/Py/LiCl. The results demonstratedthe beneficial effects of using IL/TPP media in the synthesisof PAEs, such as simplicity in operation, good yields andmoderate viscosity, shorter reaction time, not being neededto remove some chemicals (e.g. NMP, LiCl and Py), non-

Fig. 7 DSC curves of PAE(1–3)a and PAE(1–3)c under N2 at aheating rate of 10 °C/min

Table 4 Thermal properties of new synthesized PAEs

Polymer Tg (°C)a T10 (°C)

b T10 (°C)c Char yieldd LOI (%)e

PAE1a 353 487 474 77 48

PAE1b 324 475 469 64 43

PAE1c 227 461 455 33 31

PAE2a 355 498 480 78 49

PAE2b 328 482 477 66 44

PAE2c 240 479 462 34 31

PAE3a 351 472 436 68 45

PAE3b 322 465 427 53 39

PAE3c 212 460 421 25 28

PAE3a′ 351 472 430 66 44

PAE2b′ 327 480 447 65 44

PAE1c′ 225 458 429 30 30

a Glass transition temperature was recorded at a heating rate of 10 °C/minin N2

b Temperature at which 10 % weight loss was recorded by TGA in N2

c Temperature at which 10 % weight loss was recorded by TGA in aird Percentage weight of material left undecomposed after TGA analysisat a temperature of 700 °C in N2

e Limiting oxygen index percent evaluating at char yield 700 °C

PAE1a-PAE3c and PAE3a′- PAE1c′ were synthesized in IL/TPP andNMP/TPP/Py/LiCl media, respectively

Fig. 8 TGA curves of PAE(1–3)a and PAE(1–3)c under N2 at aheating rate of 10 °C/min

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volatility and reusability, as well as the environmental pol-lution. These PAEs have collection of different functionalgroups such as ether linkage, substituted imidazole and bulkypendant such as biphenyl, naphthalene and diphenyl alongtheir backbones which gave rise to restricted segmental mo-bility, so that the overall observable effect is a remaining highTg (up to 355 °C) and an enhancement in solubility in manyorganic solvents at the same time. They have exhibited highthermal stability (T10 up to 421 °C in air) because of thearomatic structure and these polymers also emitted fluores-cence light at λe.max0458–511 nm with Φf up to 35 %.

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